Chapter 10

Three stages of interphase: Most cells spend most of its life in interphase: between mitotic divisions. Three stages of interphase: G1: metabolic activities S: DNA synthesis G2: protein synthesis needed for cell division Mitosis: process of nuclear division that maintains chromosome number Cells division produces two genetically identical daughter cells Developmental processes (growth, repair and tissue remodeling) Eukaryotic asexual reproduction (offspring are produced by one parent)

Human body cells are diploid (two of each chromosomes) Homologous chromosomes: have the same length, shape, and genes During the cell cycle chromosomes are duplicated Replicated chromosome copies called sister chromatids During mitosis, the sister chromatids are pulled apart Each sister chromatid ends up in separate nuclei

Cell divison is controlled by genes Inhibitors of the cell cycle normally keep cells in G1 “Checkpoint genes” monitor if a cell is ready for division

Metaphase: all chromosomes are aligned midway between spindle poles Prophase Chromosomes condense Microtubules forming a spindle (functions to move chromosomes) Nuclear envelope breaks up Metaphase: all chromosomes are aligned midway between spindle poles 3. Anaphase: sister chromatids separate and move toward opposite spindle poles 4. Telophase: chromosomes decondense; two new nuclei form

In most eukaryotes, cytokinesis (cytoplasmic division) occurs between late anaphase and the end of telophase Microtubules pull membrane towards the center Animal cell cytokinesis: Cleavage furrow forms Plant cell cytokinesis: Disk-shaped cell plate forms and partitions with two new cell walls

Telomeres are noncoding repeat DNA sequences found at the ends of eukaryotic chromosomes Telomeres provide a buffer against the loss of more valuable internal DNA Telomeres short with each replication Checkpoint gene halt the cell cycle and if telomere are too short

Neoplasm: accumulation of abnormally dividing cells Tumor: neoplasm that forms a lump Oncogene: gene that helps transform a normal cell into a tumor cell Proto-oncogenes: gene that, by mutation, can become an oncogene Example: growth factors – molecules that stimulate mitosis and differentiation

Benign neoplasms such as warts are not usually dangerous Multiple checkpoint genes mutations are required to form a malignant cell Metastasis: process in which malignant cells spread from one part of the body to another

Chapter 11

Cells of eukaryotes normally contain pairs of homologous chromosomes (Diploid – 2n) Homologous chromosomes carry genes of the same characteristics Different forms of the same gene are called alleles

Sexual reproduction recombines the genes of two parents during fertilization. Genetic diversity offers a better chance of surviving environmental change than clones Meiosis: occurs in reproductive cells of eukaryotes Gametes: cells that are the basis of sexual reproduction All gametes (egg and sperm) are haploid (n). Derive from diploid reproductive cells Fertilization: two haploid gametes fuse - a zygote is formed The diploid chromosome number is restored

Prophase I Homologous chromosomes condense, pair up, and swap segments Spindle attach to chromosomes; nuclear envelope breaks up Metaphase I - homologous chromosome pairs are aligned midway between spindle poles Anaphase I: The homologous chromosomes separate and begin heading toward the spindle poles Telophase I: clusters of chromosomes reach the spindle poles; new nuclear envelope forms

Meiosis II is more like mitosis Sister chromatids of the unpaired chromosomes separate during Anaphase II

Two events in meiosis introduce novel combinations of alleles into gametes: Crossing over in prophase I Segregation of chromosomes into gametes Creates variation